Physiology and pathophysiology of skeletal muscle contractions

Abstract

An overview is presented of the physiology and pathophysiology of dynamic skeletal muscle contractions in the intact living organism. Dynamic muscle activities are divided into concentric contractions with shortening of muscle fibres and the production of positive work, and eccentric contractions with lengthening of muscle fibres and the production of negative work. In positive work, muscle tension overcomes external forces. In negative work, external forces overcome muscle tension. The latter phenomenon, with relatively few active motor units, explains the injuries induced by eccentric contractions. Both the contractile and non-contractile elements are involved in the muscle injuries and, clinically, they are referred to as myofibrositis.

A naturalistic study of the relationships among electromyographic activity, psychological stress, and pain in ambulatory tension-type headache patients and headache-free controls.

“…For instance, Philips (13) observed that changes in pain behavior and subjective reports of pain lagged behind changes in EMG activity during biofeedback therapy for headache. Also, Christensen (14) suggested that muscle hyperactivity causes ischemia, which results in the local release of chemical substances, that in turn cause pain. According to this model, the pain experience might be expected to lag behind an increase in EMG activity.…”

Experimental occlusal interferences. Part V. Mandibular rotations versus hemimandibular translations

“…Using observations from our previous studies (Christensen, 1986;Christensen & Hutchins, 1992;Christensen & Rassouli, 1995a,b,c;Rassouli & Christensen, 1995), we shall illustrate an imaginary, but typical, relationship between the mechanical work (force X distance) produced by the paired masseter muscles and the in vitro translatory motions of RC and LC (Fig. 1).…”

“…Although the negative work decelerating the downward translation of LC ( Fig. 1) appears small in magnitude (6-6 x 10"^ kgm), it may be sufficient to topically damage some of the sarcomeres (2-3 ym in length) of the left masseter muscle (Christensen, 1986;Christensen & Hutchins, 1992).…”

A Revised View of the Dynamics, Physiology, and Treatment of Occlusion: A New Paradigm

“…71 Motor units cycle during function. 72,73 When a motor unit works, it fatigues. 74,75 When fatigued, it drops out of the movement to rest, while a rested motor unit with a similarly oriented vector takes its place.…”